A gene from the region of the human X inactivation centre is expressed exclusively from the inactive X chromosome

X-chromosome inactivation results in the cis-limited dosage compensation of genes on one of the pair of X chromosomes in mammalian females. Although most X-linked genes are believed to be subject to inactivation, several are known to be expressed from both active and inactive X chromosomes. Here we describe an X-linked gene with a novel expression pattern - transcripts are detected only from the inactive X chromosome (X_i) and not from the active X chromosome (X_a). This gene, called XIST (for X_i-specific transcripts), is a candidate for a gene either involved in or uniquely influenced by the process of X inactivation.